





public class Solution2 {
    public class ListNode {
    int val;
    ListNode next = null;
    public ListNode(int val) {
        this.val = val;
    }
}
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    public ListNode oddEvenList (ListNode head) {
        // write code here
        if(head==null){
            return head;
        }
        ListNode even=head.next;
        ListNode odd=head;
        ListNode evenhead=even;
        while(even!=null&&even.next!=null){
            odd.next=even.next;
            odd=odd.next;
            even.next=odd.next;
            even=even.next;
        }
        odd.next=evenhead;
        return head;
    }
}